[AWDFTW]

Moved to correct forum.

 

[worrst]

When I take my foot off the gas of my Outback with the CVT it free-wheels (coasts) until about 10mph and then the transmission re-engages. Is this normal as with a shifting automatic transmission you can free-wheel all the way down to 0mph? You can feel the re-engaging and witness when you view the instantaneous drop in mph.

Re-engaging like a clutch?

 

[hadouken]

I have noticed something similar. It free wheels for a few seconds then re-engages the transmission to provide engine braking. I guess it's a tradeoff between efficiency & safety.

 

[subiesailor]

I have noticed something similar. It free wheels for a few seconds then re-engages the transmission to provide engine braking. I guess it's a tradeoff between efficiency & safety.

Nope you guys are off the mark

Fuel cut off feature now with many makes not just subaru causes much of this behavior.

When your under a specific speed the engine is running - when your at higher speeds and you coast ie no throttle input for a given period of time the fuel system cuts back to near zero these changes in fuel and engine behavior are generally felt given the transmission is connected to the engine all the time regardless.

Also the fuel systems in todays cars control just how fast fuel is fed and removed from the engine to avoid spiking emissions output - ie the electronic Nanny is tempering your throttle inputs to keep emission output on an even keel persay.

 

[kressler]

Why?

Then why does the immediate mpg reading stay at 99.9 until this happens at around 10mph and then it drops drastically as if you put your foot on the gas?

 

[subiesailor]

Then why does the immediate mpg reading stay at 99.9 until this happens at around 10mph and then it drops drastically as if you put your foot on the gas?

99.9 mpg is related to how fast your moving vs the fuel cut off feature the engine is still spinning and being driven by the transmission. When you get to 10mph fuel system comes back on and your speed is low resulting in a large drop in mileage fuel used vs speed your moving.

 

[BossMaverick]

As far as Kressler's question:
My theory is that the CVT needs to "shift" down before the car stops (much like a bicycle). A traditional automatic transmission can go into different forward gears while the vehicle is stopped but I don't see how a CVT could vary the ratio if the pulleys aren't spinning. It probably is the most noticeable at slower speeds because that is when the ratio between the engine and wheels speeds are at the highest difference. They might program it on the more aggressive side to help with brake pad life. Edited to Add: See my post below. I realized that the effect that you describe could be a combination of the CVT downshifting, fuel programming, and the VVT adjusting while the engine RPM is dropping (the VVT adjusts the advancement of the intake camshaft so you can idle smoothly yet develop more power and efficiency at operating speed RPM's).

As far as Hadouken's comment (assuming Hadouken is talking about the feeling at higher speeds and not at 10 mph or below):
My theory is that it slightly "down shifts" in preparation for you coming back on the gas so you have a quicker throttle response. This would help the driveability for driving in traffic when speeds are constantly varying. It also helps for going downhill.

I have a 6mt and I don't notice that long of a lag or varying rates of engine braking so I wouldn't think it is the fuel cut off causing these things but I wouldn't discredit that theory either (engines with CVT's would just have to have more delayed fuel cut off for this theory to be correct).

 

[BossMaverick]

99.9 mpg is related to how fast your moving vs the fuel cut off feature the engine is still spinning and being driven by the transmission. When you get to 10mph fuel system comes back on and your speed is low resulting in a large drop in mileage fuel used vs speed your moving.

Wouldn't you get less engine braking at less than 10 mph if that is when the fuel came back on? Edited to Add: I suspect the instant fuel gauge is just indicating the point in which the car is getting decent mileage while coasting to the point in which you eventually get down to 0 mph while idling. Worse fuel mileage would also come into play if the CVT is "down shifting" and using the engine more for braking effect. I'd like to know if the engine RPM increases anywhere from when the car goes from 20 mph down to 0 mph as this would help to tell if the drop in fuel mileage and braking force is a result of the CVT providing engine braking or if it is more of an effect of fuel cut off. ***Sudden brainstorm idea while writing the edit: I wonder what the VVT is doing while the car is slowing because that may play into it as well. It could really be a trifecta combination of the CVT downshifting, fuel programming, and the VVT adjusting in preparation for idle. Heck, the CVT and VVT might even be programmed to work in harmony with each other.***

Also, see my above post. I think there are two effects that were mentioned that are being discussed as only one thing. One effect that was mentioned was strong engine braking at 10 mph or less (the original post). The other effect is a time lag between free wheeling and engine braking when you coast at higher speeds (what a later post seems like at least).

 

[BossMaverick]

I know this will be three posts in a row but I'm going to try some experimenting tomorrow or Sunday. I'm going to use my Outback with the 6mt to slow to the vehicle to engine idle RPM while using varying gears. Example: Coast down in first gear until the engine hits 600 rpm (or whatever the idle RPM is for the day), then do the same thing in second gear, and then do the same thing in third gear. Here is my theory:
-An increase in engine braking at a certain non-variable speed (unrelated to transmission gear and engine RPM) will indicate software programming (like fuel programming, throttle-by-wire/throttle body programming, etc).
-An increase in engine braking at a certain engine RPM (unrelated to vehicle speed or transmission gear) will indicate something like the VVT and/or software programming.
-If there is a constant rate of engine braking all around regardless of transmission gear, vehicle speed, or engine RPM, the effect everyone here are experiencing is probably something to do with the CVT and/or software programming differences with the CVT option.

Please let me know if there are any flaws to my above theories.

I know the best testing results would for me to slow down to a complete stall and do things like unplug the VVT wiring socket but I'm not that mean to my car so I refuse to do that.

 

[napcop]

"downshifting" automatic

when i take my foot off the gas of my outback with the cvt it free-wheels (coasts) until about 10mph and then the transmission re-engages. Is this normal as with a shifting automatic transmission you can free-wheel all the way down to 0mph? You can feel the re-engaging and witness when you view the instantaneous drop in mph.

i've noticed the same thing in my cvt (2013 ob), especially for in-town slower speed driving. I try to coast to stops to save gas, but notice the downshifting feel. I've been dropping it into neutral lately to get a better "coast"... Anyone want to chime in on whether or not this is a good idea, specifically for drivetrain longevity?
[email protected]

 

[Novablue]

i've noticed the same thing in my cvt (2013 ob), especially for in-town slower speed driving. I try to coast to stops to save gas, but notice the downshifting feel. I've been dropping it into neutral lately to get a better "coast"... Anyone want to chime in on whether or not this is a good idea, specifically for drivetrain longevity?
[email protected]

I have no evidence but I'd recommend against it. Especially at higher speeds my car seems to "clunk" when I re-engage from neutral and moving. Also, if you need to emergency maneuver you'll be in neutral and that will limit your options.

If any of you are doing this only to save fuel, you really picked the wrong car.